On Oct 6, 2007, at 11:06 PM, Paul Mackerras wrote: > Kumar Gala writes: > >> In a discussion with Hollis over beer he raised the question why >> TASK_SIZE is 0x80000000 on ppc32. >> >> I was wondering if anyone know why this was still the case? Seems >> like we have a 1Gb whole between TASK_SIZE & KERNELBASE. > > Two reasons: (a) PReP used to map PCI stuff with BATs in the > 0x80000000 - 0xbfffffff region, and (b) some embedded ports with > software-loaded TLBs test just the high bit of the address to > determine whether to use the kernel or user page tables.
Can you explain (a) further -- I'm assuming the BAT mapping is 1:1 for that region? For (b) it looks like: * 40x, 44x, fsl-booke compare against TASK_SIZE in their software handlers. * 8xx still tests 0x80000000 * 6xx (603) compares against KERNELBASE It would seem like we should set the default on 8xx & PReP to 0x80000000 and not allow it to be modified since that will break the world and for everything else move it to match KERNELBASE. Any issues with that? - k _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
